1. Field of the invention
This invention relates in general to a method and apparatus for controlling sleep disorder breathing, particularly one utilizing positive air pressure supplied to a person's air passages.
2. Description of the Prior Art
The majority of patients diagnosed at sleep disorders centers in the United States suffer from excessive daytime sleepiness. The leading cause of this symptom is sleep apnea.
Sleep apnea is a potentially lethal condition characterized by multiple obstructive or mixed apneas during sleep. Symptoms are repetitive episodes of inordinately loud snoring and excessive daytime sleepiness. The characteristic snoring pattern noted with this syndrome is one in which inspiratory snores gradually increase when obstruction of the upper airway develops. A loud, choking inspiratory gasp then occurs as the patient's respiratory efforts succeed in overcoming the occlusion. The aroused patient is usually aware of neither the breathing difficulty nor of the numerous accompanying body movements that at times violently disturb his sleep. A diagnostic study is necessary for an adequate description of the patient's sleep breathing pattern.
Apneic episodes during sleep are defined as cessations of air flow at nose and mouth lasting 10 seconds or longer and can be readily documented by polysomnographic recordings. Variations in night-to-night frequency of apneic pauses exist in many patients, with increased frequency appearing to follow upper respiratory infections or use of sedating drugs or alcohol.
Treatments available for sleep apnea vary from weight loss to surgical intervention to prosthetic devices. Although weight loss is the most desirable approach, few patients are able to comply with their diets and very few can afford to continue the exposure to the symptoms of sleep apnea for six months to a year while losing sufficient weight to reduce or cure the disease. Surgical approaches are only effective in about 50% of the cases, are invasive, expensive and may produce undesirable side effects.
The most successful prosthetic device has been the nasal continuous positive airway ventilator ("CPAP"). It was initiated by a group in Australia who adapted a vacuum sweeper motor to a hose and attached it to the patient's face via a nasal mask. The advantages of the nasal CPAP system are that it produces immediate relief, is non-invasive and can be used while achieving weight loss and thus eliminating the need for surgery. The primary problem with nasal CPAP has been compliance. While nearly all of patients are fitted with nasal CPAP as an initial treatment modality, many cease using the system after about six months.
Investigation of the causes for poor compliance among patients has identified three primary factors. The first factor is the lack of perfect fit and discomfort of wearing the nasal mask. The positive pressure of the ventilator flow is often mentioned as the second factor. Some patients experience an uncomfortable and annoying sensation of forced air stream in their nose and mouth. Third, dry mouth and throat are often cited as the source of dissatisfaction with the sleep apnea ventilators.
Hypopnea is a milder form of apnea, usually referring to episodes of partial obstruction of the upper airway passages. Excessive snoring, without hypopnea or apnea occurrences, can also be a serious problem. Apnea, hypopnea, and snoring will be referred to herein as sleep disorder breathing.